1. Field of the Invention
Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for a Boiling Water Reactor (BWR) inlet mixer clamp assembly that physically restrains and applies a downward force on an inlet mixer of a boiling water reactor (BWR) jet pump assembly. The inlet mixer main clamp assembly may be used as an alternative to conventional jet pump beam assemblies. Alternatively, the inlet mixer clamp assembly may be used as a redundant physical restraint in addition to conventional jet pump beam assemblies.
2. Related Art
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends (for example by a bottom head and a removable top head). A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus between the cylindrical reactor pressure vessel and the cylindrically shaped shroud.
In a BWR, hollow tubular jet pumps positioned within the shroud annulus provide the required reactor core water flow. The upper portion of the jet pump, known as the inlet mixer, is laterally positioned and supported against two opposing rigid contacts within jet pump restrainer brackets by a gravity actuated wedge.
Conventionally, the inlet mixer is held in place by jet pump beam assemblies at the top of the BWR jet pump assembly. The jet pump beam assemblies press down and provide a clamping force on the inlet mixer to mitigate movement, rotation and vibration of the inlet mixer and reduce potential leakage between the inlet mixer and the transition piece sealing surfaces of a jet pump assembly. Additionally, the jet pump beam assemblies mitigate the potential that the inlet mixer may be ejected from the diffusers of the jet pump assembly during operation of the jet pump assembly. Conventionally, jet pump beam assemblies are highly stressed, they are limited in their clamping force, and they are susceptible to stress corrosion cracking. Field failures of jet pump assemblies have previously caused significant plant downtime and expensive repair.